Multi-piston fluid motor



July 4, 1961 A. M. BARRETT MULTI-PISTON FLUID MOTOR 3 Sheets-Sheet 1 Filed May 25, 1956 INVENTOR. Qrizurflfiarreifi M BY m. M, I

y 1961 A. M. BARRETT 2,990,813

MULTI-PISTON FLUID MOTOR Filed May 25, 1956 5 Sheets-Sheet 2 Bifm,% I

July 4, 1961 A. 'M. BARRETT MULTI-PISTON FLUID MOTOR 3 Sheets-Sheet 3 Filed May 23, 1956 Qv 'ififir Barr I BY I 69%;

INVENTOR United States Patent Ofice 2,990,813 Patented July 4, 1961 2,990,813 MULTI-PISTON FLUID MOTOR Arthur M. Barrett, Northbrook, Ill., assignor to Barrett- Cravens Company, Northbrook, 111., a corporation of Illinois Filed May 23, 1956, Ser. No. 586,816 3 Claims. ('Cl. 121-38) The present invention relates to lift trucks, particularly of the industrial type adapted for transporting loaded skids, pallets and the like in factories, warehouses and other industrial establishments.

One of the objects of the invention is to provide a lift truck of the hydraulically actuated type in which the hydraulic lifting pressure for actuating the hydraulic jack or ram is created by an improved construction of hydraulic pump and an improved operating mechanism therefor, responsive to repeated strokes of the steering handle of the truck.

Another object of the invention is to provide an improved construction and arrangement of release valve and discharge valve for the hydraulic system. The release valve is responsive to the manual opening for lowering the load, and the discharge valve is regulatable or adjustable for controlling the rate of descent of the load. The release valve and the regulatable discharge valve are both combined in a single assembly, which simplifies the construction, reduces cost, and provides a very efficient and compact working relation.

Another object of the invention is to provide an improved multiple speed hydraulic ram for effecting the lifting and lowering of the lifting frame relatively to the wheeled frame of the truck. This multiple speed ram has two piston areas so constructed and arranged that the ram automatically transposes from a single piston area to a double piston area at an intermediate transition point in one direction of movement of the ram, and automatically transposes back from a double piston area to a single piston area at this same transition point in the other direction of movement of the ram. In the load lifting operation, the double piston area is effective at the start of the lifting operation, when the greatest lifting effort is necessary, and the single piston area is effective at the conclusion of the lifting operation when a reduced lifting effort is adequate. In the load lowering operation, the single piston area is effective at the start of the lowering operation, when a reduced lowering effort is adequate, and the double piston area is effective at the conclusion of the lowering operation when the greatest lowering effort or retardation is necessary.

Other objects, features and advantages of the invention will appear from the following detail description of one preferred embodiment thereof. In the accompanying drawings illustrating such embodiment:

FIGURE 1 is a fragmentary side elevational view of my improved lift truck;

FIGURE 2 is "a fragmentary plan view of the truck,

part of the frontend being shown in section, and the intermediate portions of the lifting frame and wheeled frame being broken away;

FIGURE 3 is a fragmentary view showing the horn, motion transmitting link, rocker arm and rock shaft for transmitting pumping motion from the steering handle of the truck to the hydraulic pump;

FIGURE 4 is a fragmentary side elevational view of the hydraulic pump and reservoir showing the crank connection between the rock shaft and pump plunger, and showing the operative connection between the release valve and the release treadle;

FIGURE 5 is a vertical sectional view through the hydraulic pump and through the release valve and discharge valve assembly;

FIGURE 6 is a horizontal sectional view taken approximately on the plane of the line 6-6 of FIGURE 5, showing the release valve and discharge valve in horizontal section, and showing the oil return passageway from the release valve to the liquid reservior;

FIGURE 7 is a vertical transverse sectional view taken approximately on the plane of the line 7-7 of FIGURE 5, and showing the inlet valve passageway from the reservoir to the hydraulic pump; and

FIGURE 8 is an axial sectional view through the twospeed or dual piston ram.

My improved lift truck comprises the conventional upper lifting frame 11 and lower wheeled frame 12, the latter frame being mounted on a pair of steerable front wheels 13 and a pair of rear wheels 14. The two frames Hand 12 are connected together by front and rear pairs of vertically swinging links 15 and 16, which provide for the lifting and lowering movement of the lifting frame 11 relatively to the wheeled frame 12. The front links 15 have their upper ends pivoted to the lifting frame 11 on transverse pivots 17, and have their lower ends pivoted to the lower wheeled frame 12 on transverse pivots 18. The rear links 16 have their upper ends pivoted to the lifting frame 11 on transverse pivots or on a transversely extending pivot shaft 21, and have their lower ends pivoted to the lower wheel frame 12 on the axle 22 on which the rear wheels 14 are journaled.

As shown in FIGURE 2, the upper lifting frame 11 hasits side bars flared outwardly at 11 to a width greater than the span of the rear wheels 14, the rear ends of these side bars being bent inwardly and welded together at 11". Two angle bars 23 and 24 have their ends welded between the flared portions 11' of the side bars. Mounted on the under side of the rear angle bar 24 are the transverse pivots or transverse pivot shaft 21 for the upper ends of the links 16.

The lower wheeled frame 12 has its side bars converged inwardly at 12 to a width less than the span of the rear wheels 14, the rear Wheel axle 22 being passed through these inwardly converged portions of the lower frame bars 12'. A reinforcing cross member 26 has its ends welded to the converged side bar portions 12' of the lower frame.

Secured to the front end of the lower frame 12 is a transverse yoke-shaped casting 30. This casting is secured to the side bars 12 of the lower frame byrthe pivot bolts 18 and also by bolts 31 which pass through the frame side bars 12 and engage in inner side arms 32 extending rearwardly from the casting 30. Formed medially in the raised central portion of the yoke 30 is a vertically extending bearing boss 34 in which a vertically extending king bolt 35 is journaled. Secured to the lower end of the king bolt 35 on the under side of the yoke 30 is a turntable 36 from which extend stub axles on which the steerable front wheels 13 are journaled. Secured to the upper end of the king bolt 35 above the yoke 30 is a steering head or collar 38 formed with a forwardly and upwardly extending pivot bracket 39. This pivot bracket 39 carries a transverse pivot pin 41 on which the steering and lifting handle 42 of the truck is pivotal-1y mounted. The handle 42 is swung down to a forwardly extending position when it is being used to tow and steer the truck, and when the handle is in this position .it is sub stantially counterbalanced through the instrumentality of a compression spring 43 and counterbalancing rod 44 connected between the pivot bracket 39 and the handle, substantially as disclosed in my prior Patent 2,358,957.

The steering lever 42 is also adapted to transmit repeated strokes to the hydraulic pump of the lifting mechanism through the instrumentality of a pumping lever or shackle member 4 which has a forwardly extending lower portion that is ,pivotally mounted on the steering handle pivot pin 41. The upper end of the pumping lever 48 has a nose 49 over which is adapted to hook a latch 51 that is pivotally mounted on the towing lever 42, this latch 51 being manually releasable from the pumping lever 48. Engaging over the lower portion of the pumping lever 48 is a circular eye 54- from which extends a socket 56 into which threads the upper end of a drag link 57. The eye 54 normally occupies a position substant-ially concentric of the steering axis of the king bolt 35 to accommodate steering movement. This operating relation relation of shackle member 48, latch 51 and motion transmitting eye 54 is substantially in accordance with the constructions disclosed in my prior Patents Nos. 1,707,971, 1,773,934, 1,803,688, 1,829,726, etc. By virtue of this operating relation, up and down stroking motion of the handle 42 is transmitted to the link or rod 57 as backward and forward reciprocating motion.

Referring to FIGURE 3, the link or rod 57 has pivotal connection with a crank arm 61 which is secured to a transverse rock shaft 62 that has its ends journaled in bearings carried by the side bars of the lower frame 12. The crank arm 61 comprises a pair of laterally spaced plates 61' which have their lower ends welded to the rock shaft 62. Welded between the upper ends of these plates 61 is a section of angle bar 64 having an aperture 65 therein through which passes the rod 57. Mounted on the rod 57 and engaging the inner or back side of the angle bar 64 is an apertured bearing guide 66 of tapered cylindrical form, and screwing over the threaded lower end of the rod 57 beyond this apertured guide 66 are lock nuts 68. It will be evident that stroking motion of the truck lever 42 is transmitted as a rocking motion to rock shaft 62 through rod 57 and crank arm 61, so long as latch 51 remains in latching engagement with the shackle lever 48. Release of the latch 51 enables the truck lever 42 to be swung down to a forwardly extending towing and steering position for maneuvering the truck.

Referring to FIGURES, 4 and 5, the rocking motion of the rock shaft 62 is transmitted to plunger 71 of a hydraulic pump 72 through the medium of a rocker arm 73. This rocker arm preferably comprises a pair of spaced plates 73' having their lower ends welded to the rock shaft 62 and carrying a pivoted roller 75 between their upper ends, which roller transmits inward thrusting motion to the outer end of the plunger 71.

The hydraulic pump 72 is defined within a combined pump and reservoir casting 77 which is secured to a platform plate 78 extending between the side bars of the lower frame 12, the casting 77 being provided with threaded sockets 79 for receiving fastening screws passing up through the platform plate 78., The pump plunger 71 enters a horizontal cylinder 81 in the casting 77 through a seal or packing gland comprising outer and inner compression sleeves 83 and 84 between which is compressed a plurality of pliable sealing rings 85. These sealing rings 85 may be composed of neoprene, leather, or any other suitable material, and are preferably of V or chevron-shaped cross section, so that the pressure of leaking oil will tend to expand them tighter into engagement with the plunger 71 and cylinder bore 81. The outer sleeeve 83 is held against outward displacement by a snap retaining ring 88, and the inner sleeve 84 is constantly urged in an outward direction by a compression spring 89 within the cylinder 81. The plunger 71 is also urged in an outward direction by a centrally disposed compression spring 91 which has its rear end entering a counterbore 92 formed in the inner end of the plunger 71. The front ends of the two compression springs 89 and 91 abut against a cylinder closure plug 93 which fits into a reduced outer end 94 of the cylinder 81. An O-ring 95 is confined between the cylinder and the closure plug to maintain an effective seal between these two.

Formed in the casting 77 to one side of the cylinder 81 is a liquid reservoir 101 which serves to contain the oil or other hydraulic liquid used in the hydraulic system. An oil inlet passageway 103 extends from the reservoir 101 and opens into a larger bore 104 communicating with the cylinder 81. A spring pressed inlet ball 105 seats against the end of the passageway 103 and functions as an inlet valve for the hydraulic pump. Leading from the upper part of the cylinder is an outlet passageway 107 which opens into a vertical counterbore 108. A gravity held ball check 109 seats against the upper end of the passageway 107 and functions as an outlet valve for the cylinder. The vertical outlet passageway 108 opens into a horizontal bore 111 and thence communicates through another vertical passageway 112 with an angle nipple 113 which screws into the passageway 112. The angle nipple 113 connects through the tube or pipe 114 with the hydraulic lifting and lowering ram 115, which will be later described.

Referring now to the improved release valve and discharge valve assembly, this assembly is mounted in the horizontal bore 111 and in a series of counterbores extending coextensively from the bore 111. -For example, there is formed coextensive with the bore 111 a first counterbore 116, a second counterbore 117 and a third threaded counterbore 118. Extending axially through these counterbores and into the inner bore 111 is a tubular valve stem or barrel 120 which has a tapered inner valve surface 121 adapted to coact with a tapered valve seat 122 formed at the inner end of the bore 111, such valve surface 121 and valve seat 122 constituting the regulatable discharge valve, as will be presently described more in detail. The valve stem or barrel 120 has an inner reduced portion 124, and an intermediate threaded portion 125. Fitting over the inner reduced portion 124 is a metallic packing washer 126 which seats in the bottom of the first counterbore 116. Abutting this packing washer 126 is a ring washer 127 composed of pliable sealing material. Abutting the outer side of this sealing washer 127 is a thimble ring 12 8 having its inner end of a diameter to effect a snug sliding fit within the first counterbore 116, and having its outer end of a diameter to effect a snug sliding fit within the second counterbore 117. This thimble ring is provided with an internal groove from which lead ports 131 opening into the second counterbore 117, which in turn is connected by a passageway 132 with the liquid reservoir 101, such arrangement of ports and passageways providing for the return flow of liquid to the reservoir when the release valve is opened. Abutting the outer end of the thimble ring 128 within the second counterbore 1 17 is a pliable packing or sealing washer 134. Abutting the outer side of this sealing washer 134 is a gland sleeve or thimble 135 which has an external thread 136 screw-ing into the threaded counterbore 118. Screwing this gland sleeve 135 inwardly compresses the outer sealing washer 134, and, through the medium of the thimble ring 128, it also compresses the inner sealing washer -127. Formed in the outer portion of the gland sleeve 135 is a threaded counterbore 137 into which screws the thread '125 on the outer portion of the valve stem or barrel 1 20. Rotating the stem or barrel 120 within the sleeve 135 screws the inner valve surface 121 toward or away from the tapered valve seat 122 for regulating the rate of discharge flow through the release valve.

Sliding within a large bore 139 in the outer portion of the stem 120 is a release valve plunger 140. An O-ring 141 in a groove 142 in the plunger seals the plunger against outward leakage of liquid. The plunger has a first reduced extension 143, and surrounding this extension within the bore 139 is a compression spring 144 which normally holds the plunger thrust outwardly into the position shown. A second reduced extension 146 of the plunger passes through an inner small bore 147 in the stem 120, and is adapted to unseat a spring pressed ball valve 148 from its seating engagement against the inner end of this small bore 147. The ball valve 148 is disposed at the inner .end of an enlarged counterbore 149,

and isnormally held pressed against the end of the small bore 147 by a compression spring 151 whichhas its outer end reacting against a snap ring 152 engaging in the outer end of the counterb'ore 149. Ports 154 (FIGURE 6) establish communication from the small bore 147 on the back side of the valve 148 through the ports 131 of the thimble ring 128 with the oil return passageway 132 which leads back to the reservoir. Unseating the release valve 148 thus allows oil to flow back from the hydraulic ram into the reservoir.

The release valve plunger 140 is arranged to be actuated by a release treadle 157 (FIGURE 4) which is disposed in a conveniently accessible position at the front end of the lift truck. This release treadle constitutes part of a bell crank lever which is pivotally mounted on a pivot pin 159 which extends between pivot lugs 161 projecting rearwardly from the yoke casting 30. A downwardly extending arm 158 'of this treadle lever imparts inward thrusting motion to the release plunger 140 when the treadle is depressed. The inward thrusting motion of the release plunger 140 pushes the release ball valve 148 off of its seat, and permits a return flow of the oil from the hydraulic ram 115 through the discharge valve 121122 and thence through counter-bore 149, inner bore 147, ports 154 and passageway 132 to the reservoir.

The user of the truck may by turning the stem 120 in one direction or the other either reduce or increase the constricted opening 121 -122 to the point where his average load lowers at the speed that suits him best. Flat spots 163 are splayed on the outer end of the stem 120 for the convenient reception of an adjusting wrench, and the stem is readily accessible. The sealing washers 127 and 134.:being compressed, prevent the stemo'r barrel 120 from creeping and thus changing the relief valve setting.

Referring now to the hydraulic ram 115 which constitutes 'one of the improved features of the present invention, it will 'be seen from FIGURE 8 that this ram comprises a cylinder 165 from the upper end of which extends a piston rod 166. The lower end of the cylinder 165 has a vertically swiveling connection with a trans.- verse frame member 167 which is secured between the side bars of the lower frame 12. This swiveling connection comprises a mounting plate 168 having on its upper side a cylinder head 169 which is welded into the lower end of the cylinder, and having in its lower side a spherically-shaped depression 171. This sphericallyshaped depression has ball and socket mounting on a ball extension 172 projecting forwardly from the transverse frame member 167. Also formed in the mounting plate 168 are apertures 173 through which pass bolts or studs 174 projecting forwardly from the frame member 16']. These bolts or studs permit the required amount of limited tilting movement of the cylinder 165 as the lifting frame 11 swings upwardly and downwardly relatively to the wheeled frame.

The upper end of the piston rod 166 has a similar swiveled coupling to a transverse frame member 176 extending between the side bars of the upper lifting frame 11. The upper end of the piston rod 166 has secured thereto a coupling head 177 provided with a spherically-shaped socket 178 in its upper surface. This socket has a ball and socket fit over a ball surface 179 projecting rearwardly from the transverse frame member 176. Bolts or studs 181 extend rearwardly from the frame member 176 and pass through holes 182 in the coupling head, these bolts permitting the required amount of angular tilting motion of the piston rod 166 relatively to the upper frame 11 in the lifting and lowering movement of the said frame.

The cylinder 165 has a length substantially exceeding the total stroke of the piston rod 166 so as to provide for a piston rod guide 185 in the head end of the cylinder. The outer end of this piston rod guide abuts a snap re- 6 tainer ring 186 which snaps into an internal groove 187 in the cylinder. The inner end of the piston rod guide abuts a stop sleeve 188 which is suitably secured inside the upper end of the cylinder. An air venting passageway 189 leads from the under side of the piston rod guide to an external groove 191 therein which registers with an atmospheric port 192 in the wall of the cylinder.

The lower portion of the piston rod 166 has a reduced end 193 which has a drive fit or a threaded fit into the upper end of a long narrow piston 194. Interposed between the upper end of the piston 194 and the shoulder 195 defined at the upper end of the reduced portion 193, is a stop collar 196 which, together with the piston 194, can pass up into the cylindrical space within the stop sleeve 188. However, this stop collar 196 is of larger diameter than the piston 194 so as to define an overhanging ledge or shoulder .197 projecting outwardly beyond the upper end of the piston 194, this ledge or shoulder constituting a movable abutment shoulder against which engages the supplemental piston now to be described.

The main piston 194 is of a diameter substantially smaller than the diameter of the cylinder 165, and interposed between this main piston and the cylinder is a supplementary piston 200. This supplementary piston 200 comprises upper and lower metallic sleeves or rings 201 and 202 between which is confined a pliable packing. This packing is preferably made up of a plurality of rings 203 composed of neoprene, leather, or other suitable packing material, and preferably being of V-shaped or chevron cross section, facing in a direction to be expanded by any oil tending to leak upwardly along the piston 194. The main piston 194 extends down beyond the lower end of the secondary piston 200 a substantial distance, and surrounding this lower end of the main piston is a compression spring 205 which reacts between the lower end of the cylinder 165 and the lower sleeve 202 of the supplemental piston. This spring 205 normally maintains the packing rings 203 under continuous pressure, and it also assists the hydraulic pressure in compelling the supplemental piston to follow the upward movement of the main piston. The tube or pipe 114 leading from the hydraulic pump 72 enters the lower end of the cylinder 165 through a threaded boss 206.

In the operation of my improved two-speed or double piston hydraulic ram 115, when oil enters the lower end of the cylinder from the hydraulic pump it is effective on the area of the inner piston 194 and also on the area of the outer piston 200. The thrust of the outer piston is transmitted to the piston rod through the shoulder 197 on collar 196 and thence through shoulder 195 to the piston rod 166. It is at the start of the lifting operation, when the lifting links 15, 16 are inclined more toward the horizontal, that the greatest li-fting effort is necessary. As the lifting frame 11 and its load move upwardly toward a position where the lifting links 15, 16 are more nearly vertical, a lesser lifting effort is necessary, and at this time the upper edge of outer piston ring 201 strikes the shoulder 188' at the lower end of stop sleeve 188. Thereupon, further load lifting movement of the outer piston 200 is positively arrested, with the result that the remaining lifting movement is performed solely by the inner piston 194. The transition point where double piston operation transposes into single piston operation canbe arranged to occur at any point in the stroke of the piston rod, depending upon the length of the stop sleeve 188.

In the reverse operation of lowering the lifting frame 11 and its load, the checking or retarding effect to be exerted by the ram starts at a relatively low value and then increases as the load approaches its lowermost position. At the start of the lowering operation the oil checking retardation is effective only across the area of the inner piston 194, but as soon as the shoulder 197 of collar 196 engages ring 201, the outer piston 200 is picked up for concurrent travel with the inner piston, thereby increasing the elfective area over which the oil pressure can act. As illustrative of typical proportions and operating conditions in one embodiment of my improved ram, I have successfully used a constructon wherein the inner piston 194 has an efiective area of approximately 1.225 square inches, and wherein the two pistons 194 and 200 together have a combined efiective area of approximately 2.07 square inches. With these proportions of piston areas, and with an oil pressure of approximately 3,000 pounds per square inch, the ram will exert substantially over 6,000 pounds pressure in the double piston phase of operation, and will exert only about 3600 pounds pressure in the single piston phase of operation.

While I have illustrated and described what I regard to be the preferred embodiment of my invention, nevertheless it will be understood that such is merely exemplary and that numerous modifications and rearrangements may be made therein without departing from the essence of the invention.

I claim:

1. Hydraulic apparatus of the class described comprising a cylinder, a main piston in said cylinder of smaller diameter than said cylinder, a supplemental piston between said main piston and said cylinder, cooperating thrust shoulders on said main and supplemental pistons for transmitting thrust from said supplemental piston'to said main piston during part of the stroke of said main piston, stationary stop shoulder means for interrupting the motion of said supplemental piston during the remaining part of the stroke of said main piston, said supplemental piston comprising outer and inner sleeves, packing means between said sleeves, and a compression spring in said cylinder pressing constantly against said inner sleeve.

2. Hydraulic apparatus of the class described comprising a cylinder, a main piston in said cylinder of smaller diameter than said cylinder, a supplemental piston between said main piston and said cylinder, cooperating thrust shoulders on said main piston and on said supplemental piston for transmitting thrust from said supplemental piston to said main piston during part of the outward stroke of said main piston, stationary stop shoulder means for arresting the motion of said supplemental piston during the remaining part of the outward stroke of said main piston, said supplemental piston comprising outer and inner sleeves, packing rings between said sleeves, and a compression spring in said cylinder surrounding said main piston and pressing constantly against said inner sleeve to hold said packing rings compressed, said main piston being of suflicient length to remain in sealing engagement with said packing rings during the remaining part of the outward stroke of said main piston while said supplemental piston stands arrested.

3. Hydraulic apparatus of the class described comprising a cylinder, a head guide in one end of said cylinder, a piston rod entering said head guide and having guided engagement therein, a main piston mounted on the inner end of said piston rod, said main piston being of smaller diameter than the internal diameter of said cylinder, a supplemental piston surrounding said main piston and engaging the inner wall of said cylinder, a thrust transmitting shoulder at the outer end of said main piston projecting outwardly therefrom, said supplemental piston being adapted to transmit outward thrust to said thrust transmitting shoulder during part of the outward stroke of said main piston, a stop sleeve in the outer portion of said cylinder defining a stop shoulder for arresting the motion of said supplemental piston during the remaining part of the outward stroke of said main piston, said supplemental piston comprising outer and inner sleeves surrounding said main piston, packing rings between said sleeves, and a compression spring in said cylinder surrounding said main piston and pressing constantly against said inner sleeve for holding said packing rings compressed, said main piston being of sufiicient length to remain in sealing engagement with said packing rings during the remaining part of the outward stroke of said main piston while said supplemental piston stands arrested.

References Cited in the file of this patent UNITED STATES PATENTS 1,773,935 Barrett Aug. 26, 1930 2,329,044 Gollmer Sept. 7, 1943 2,329,145 Stuebing Sept. 7, 1943 2,358,957 Barrett Sept. 26, 1944 2,464,962 Bent Mar. 22, 1949 2,620,631 Denton Dec. 9, 1952 2,659,307 Framhein Nov. 17, 1953 2,691,963 Seng Oct. 19, 1954 2,716,965 Klamp Sept. 6, 1955 2,747,550 Cosgrove May 29, 1956 2,766,591 Fawick Oct. 16, 1956 2,803,224 Wilson Aug. 20, 1957 2,893,357 Clarke July 7, 1959 

